Perhaps it's worth thinking about why we want communities to grow big at all. I think things go wrong when two different sets of incentives are muddled. The first are those that lead to a great community. The second are those that lead to a successful business built on providing a platform for a community. The business wants the community to grow because larger communities mean more revenue. But larger doesn't mean better from the community's perspective; it often means completely changing the community's character. There are probably tens of thousands of small self-organized, self-policing communities on the web that are doing fine because they don't have the business incentive to scale.
For many people, growth of "their" community provides much-desired social validation. Whatever modern terms you might use to describe this ("money", "success", "popularity", "coolness", etc.), it seems to be a far-older human need. One often tied to the need for security - so trying to dismiss it, or deal with it ever-so-rationally, is generally a mistake.
